Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.52	12.489%	$99.5753	$99.58	$99.60	$99.60
Purchase #2	$57.33	4.851%	$60.1111	$60.11	$60.10	$60.10
Purchase #3	$67.89	6.708%	$72.4441	$72.44	$72.45	$72.40
Purchase #4	$187.93	4.575%	$196.5278	$196.53	$196.55	$196.50
Purchase #5	$119.66	4.576%	$125.1356	$125.14	$125.15	$125.10
Purchase #6	$66.47	13.576%	$75.494	$75.49	$75.50	$75.50
Purchase #7	$193.83	9.330%	$211.9143	$211.91	$211.90	$211.90
7 purchase totals =	$781.63		$841.2022	$841.20	$841.25	$841.10